1. Field of the Invention
The present invention relates generally to switches and more particularly to automatic time switches which are operable in a two wire installation.
2. Description of the Prior Art
Considerable power is wasted when lights are left on needlessly. A frequent source of such waste is in offices in which lighting is inadvertently left on over night or worse, over the weekend.
Often times lights are purposely left on 24 hours a day to make a building appear occupied and thus discourage burglars. Twenty-four hour operation, however, not only wastes considerable energy during daylight hours, but can, in and of itself indicate that the building is unoccupied since most lighting is turned off during the day and very late at night. Further, when residential lighting is on, it is usually on only intermittently.
Prior art timing devices exist which can sequence a load such as turning a table lamp on and off at preset times. Most commonly, these devices are electromechanical in nature utilizing a clock type motor to trip a switch at one or more preset times.
Although useful for controlling table lamps and the like, common wiring practice often makes the use of these prior art timing devices for controlling the main lighting impractical. When a wall switch is connected in series with a ceiling light between the hot and neutral wires of the AC line, under common wiring practices, only two wires need be run to the switch. Since the second AC power line is usually not available at the switch location, without rewiring, prior art timing devices which require both AC lines to operate the clock motor may not conveniently be used to replace the wall switch.
Additionally, these prior art timing devices typically do not provide a convenient means for manually controlling the operation of the light in the traditional fashion.